DESCRIPTION (Verbatim from the application): The importance of the endothelial cell (EC) lining of the blood vessel in the regulation of vascular tone is clearly established. Hormones such as acetylcholine, substance P and bradykinin relax blood vessels in the presence of the endothelium but not in its absence. This relaxation is attributed to the release of endothelium-derived relaxing factor (EDRF). There is now evidence for multiple EDRFs. One is nitric oxide (termed NO-EDRF). In addition, there is an EDRF released by arachidonic acid (AA-EDRF) that is not PGI2 but a lipoxygenase metabolite. We have identified this AA-EDRF as a metabolite of 1 5-lipoxygenase, 11(S),12(S), 1 5(S)-trihydroxyeicosatrienoic acid (11,12,1 5-THETA), using bioassay, HPLC, chemical synthesis and gas chromatography/mass spectrometry. 15(S)-Hydroxy-1 1,12-epoxyeicosatrienoic acid (15-H-i i,12-EETA) is thought to be the precursor of 11,12,15-THETA. Both 15-H-i 1,12-EETA and 1 1(S),12(S),15(S)-THETA relax the rabbit aorta and one or both represent AA-EDRF. The proposed studies will test the hypothesis that arachidonic acid is metabolized by the endothelium to vasodilator eicosanoids, 15-H-i 1,12-EETA and 11,12,15-THETA, that are involved in the regulation of vascular tone and contribute to the action of vasoactive hormones. Studies will be conducted in isolated blood vessels, smooth muscle cells and ECs. Using chemical, analytical, biochemical, electrophysiological and pharmacological approaches, the proposed experiments will 1. determine if 15-H-11,12-EETA or other HEETAs are produced by the aorta and ECs and determine the biologically active stereoisomer of 15(S)-H-11,12-EETA. Experiments will compare the vasodilator activity of the biological and synthetic stereoisomers. 2. develop an assay for 11,12,15-THETA and investigate the regulation of 15-H-11,12-EETA and 11,12,15-THETA release by vasoactive agents and inhibitors of arachidonic acid metabolism. This quantitative data will be combined with physiological and pharmacological studies to determine the contribution of the THETA and HEETA to vascular tone and the activity of vasoactive hormones. 3. study the role of 15-lipoxygenase-1 and -2 in the biosynthesis of 15-H-11,12-EETA and 11,12,15-THETA and their degradation by 15-hydroxy PG dehydrogenase using purified enzymes, antibodies and inhibitors. 4. investigate the mechanism of smooth muscle dilation by 15-H-11,12-EETA and 11,12,15-THETA by determining their action on membrane potential and potassium channel activity.